The present disclosure relates to an image forming apparatus including a cleaning device cleaning a toner remained on an intermediate transferring belt used for intermediate transfer of a toner image.
An image forming apparatus, such as a copying machine or a printer, forming an image onto a sheet by electrographic manner carries out development by using a toner. To an electrostatic latent image formed on an image carrier, such as a photosensitive drum, the toner is supplied from a developing device and a toner image is developed. The toner image is transferred onto a sheet as a recording medium. The sheet having the toner image transferred is heated and pressured by a fixing device. Thereby, the toner image is fixed onto the sheet and the image is formed on the sheet. Thus, a series of image forming operation is completed.
As a manner transferring the toner image onto the sheet, there are a dynamic transferring manner and an intermediate transferring manner. The dynamic transferring manner is a manner transferring dynamically the toner image, which is formed onto the photosensitive drum as a transferring body, onto the sheet. On the other hand, the intermediate transferring manner is a manner transferring (first-transferring) once the toner image, which is formed onto the photosensitive drum, onto the intermediate transferring belt and then transferring (second-transferring) the toner image onto the sheet. In any transferring manner, if the toner scattering to the transferring body and non-transferred toner are remained, quality of the formed image is degraded. Therefore, the image forming apparatus includes a cleaning device removing the remained toner from the transferring body.
The cleaning device included in the intermediate transferring type image forming apparatus rotates a fur brush roller having bias applied, thereby removing the toner remained on the intermediate transferring belt by physical scraping force and electrostatic force of the fur brush roller. The removed toner is moved to an electrically charged collecting roller coming into contact with the fur brash roller and being rotated. The moved toner is stripped by a blade coming into contact with the collecting roller and collected into a waste toner box.
In such a cleaning device, in a case where a quantity of the toner adhered on the fur brush roller is large or a case where a charged amount of the toner is small, the toner is accumulated on the fur brush roller. If the toner accumulated on the fur brush roller is increased, a phenomenon where an unnecessary toner is moved from the fur brush roller to the intermediate transferring belt in reverse is caused. By adhering of the unnecessary toner onto the intermediate transferring belt, the toner image transferred onto the sheet is soiled by the unnecessary toner. If the soiled toner image is fixed onto the sheet, a problem that quality of the formed image is degraded is caused.
As a conventional technique for this problem, there is a way removing the remained toner from the intermediate transferring belt by heightening rotational speed of the fur brush roller in a case where the toner image with high concentration is formed onto the intermediate transferring belt.
In a case where the sheet which the toner image is transferred is thick, in order to heat the sheet to temperature where the fixing device can fix the toner image, the fixing device conveys the sheet at speed slower than usual. In this case, traveling speed of the intermediate transferring belt at an upstream side of the fixing belt is lowered, too. When a difference between relative speeds of the intermediate transferring belt and fur brash roller becomes large, the intermediate transferring belt is damaged by the fur brash roller. In order to prevent the intermediate transferring belt from being damaged, the rotational speed of the fur brush roller is lowered, too. If the rotational speed of the fur roller brush is lowered, centrifugal force of the fur brush roller is weakened, movement of the toner to the collecting roller is stagnated and collecting capacity is deteriorated. As a result, a quantity of the toner accumulated in the fur brush roller is increased.
In a case where transferring of the toner image onto the thick sheet is carried out successively or a case where the number of transferring the toner image onto the thick sheet is larger than the number of transferring the toner image onto the sheet with usual thickness, if the transferring onto the sheet with usual thickness is carried out after the transferring onto the thick sheet, the following problem is caused. That is, when the toner image is transferred onto the sheet with usual thickness, the speed of each component, such as the intermediate transferring belt, is returned to original speed. In such a case, when the fur brush roller is rotated at usual speed, the centrifugal force becomes stronger than that at low speed. The toner accumulated excessively in the fur brush roller may be discharged to the intermediate transferring belt before the toner is collected by the collecting roller. The toner image is transferred onto the intermediate transferring belt soiled by the discharged toner. In such a case, a problem that the quality of the image formed onto the sheet is degraded is caused.
Moreover, in a conventional technique, the rotational speed of the fur brush roller during cleaning is determined regardless of a frictional wear state of the fur brush roller rubbed to the intermediate transferring belt and collecting roller. Therefore, new problems that frictional wear of the fur brush roller is progressed and the toner is moved from the fur brush roller to the intermediate transferring belt in reverse are caused.